So immunity is really only PART of the body's defence mechanisms- the part that targets SPECIFIC pathogens or foreign particles.

The body has a natural barrier- the skin - a thick, continuous, keratinised barrier that protects it from patogens. Natural openings are protected by mucus secretions and ciliated epithelia.

If the above barriers are penetrated the body first responds with innate (non-specific) defence mechanisms mentioned above.

If the non-specific mechanisms prove to be insufficient, the body responds with adaptive defence mechanisms (immunity). Immunity is the second line of defence after phagocytosis and is defined as the ability to recognise a SPECIFIC forgien bodyand destroy it with great speed and effectiveness

There are 2 types of immunity: 1. Humoral Immunity (B-cells make antibodies. These antibodes are made to have receptors that recognise specific antigens on the pathogen and lead to it's destruction (usually by the action of phagocytes but thats not imporatant )2. Cellular Immunity (T-cells destroy infected body cells and tumour cells by lethal hit)

B-cells and T-cells are both lymphocytes made in the bone marrow. The thymus gland is essential in the development of T-cells.